Physical examinations are required or desirable in a variety of situations. In the past, complete physical examinations have been generally geared towards disease detection rather than towards evaluating the functional, e.g., aerobic and anaerobic, capacity of the human body. To some people, particularly those in low disease risk groups, the fact that no disease is found during an examination may not be a motivating enough reward to take a physical examination. It is believed that meaningful tests of functional capacity as part of a physical examination may encourage more people to take physical examinations because the results of such tests are of practical value that can be used to set functional capacity goals. Thus, the physical examination becomes a vehicle for improvement as well as a disease detection procedure.
Human functional capacity tests have been generally oriented to aerobic capacity with little attention or emphasis having been given to the anaerobic capacity other than as it relates to aerobic activity. Aerobic and anaerobic capacity reflect the condition of a subject's aerobic and anaerobic metabolisms, respectively. Aerobic metabolism refers to the body's method of producing energy by a process requiring oxygen. Whenever the available amount of rate of oxygen-based energy is exceeded, an anaerobic state is entered in which energy is produced by a process that does not require oxygen, but may result in oxygen debt. Thus, aerobic and anaerobic metabolism are related but separate functions. Capacity in this sense refers to some measure of the metabolism's overall ability to produce energy. For example, a time value indicative of the time it takes under given conditions to deplete the subject's energy production to zero is one measure of capacity.
It is of value to distinguish the aerobic metabolism energy sources from anaerobic metabolism energy sources. Muscles contract from phosphorylation of adenine triphosphate (ATP). Metabolic energy sources replenish the ATP when sustained or repeated muscle contractions occur. Aerobic oxidative phosphorylation provides ATP at a steady rate until the energy reserves of glycogen or fatty acids are depleted. At this point, or just prior to this point, anaerobic metabolism begins. Also, anaerobic metabolism is also called upon when higher levels of mechanical work are required. The anaerbic metabolism sources of ATP are less efficient, require more caloric energy to produce ATP, are depleted sooner, and produce an oxygen debt.
Muscle contraction can also be viewed in terms of the behavior of the nerve-muscle combination called the motor unit. There are three types of motor units: I, IIA, and IIB. Type I motor units draw energy from aerobic metabolism. Type IIA motor units draw energy from aerobic and anaerobic lactate metabolism. Type IIB motor units draw energy aerobic and anaerobic lactate metabolism, plus creatinine phosphatase enzyme metabolism. Type IIB motor units are brought into action only when a higher force of muscle contraction takes place. Training of motor units is specific since only those units trained will respond. With respect to performance, the creatinine phosphate production of ATP is brief and is believed to deplete in 10-15 seconds under maxiumum loads. The lactate system is believed to deplete in 5-15 minutes under maximum loads.
Interest in aerobic exercise and fitness has naturally evolved from interest in cardiac output evaluations since a decrease in cardiac output can reflect coronary artery deterioration. If the cardiorespiratory and mechanical efficiency of a subject remains unchanged, the oxygen consumption of the subject during exercise relates directly to the cardiac output. To test the aerobic capacity of a subject, a standard treadmill stress test is often used. The aerobic work performed during the treadmill test is directly related to oxygen consumption and thus to cardiac output. The aerobic exercise level achieved and measured on the test is commonly used as the basis for estimating cardiac output. Using such tests, oxygen consumption and cardiac output are indirectly measured by measuring the aerobic treadmill performance. Such tests do not generally measure anaerobic parameters.
At least two categories of anaerobic metabolism are known and are important in their own right. These are anaerobic peak power output and anaerobic capacity. Anaerobic test systems that provide a method for testing power and capacity have been devised. A common test for estimating anaerobic power is a 30-second bicycle ergometer test. In this test, the subject pedals an exercise bicycle as fast as possible with a measured fixed load for 30 seconds. Values for the RPM of the bicycle pedal during the test are combined with a value for the load imposed on the subject by the exercise device to produce a set of derived power values over the test period. The power values calculated for each 5-second subinterval are averaged over the 30-second test period to produce an average power value. In one test, an anaerobic capacity parameter is defined as the average power value for a test period. In the same test, a peak power parameter is defined as the highest power value for a five-second subinterval that is measured during the test period. Unfortunately, this test protocol has a number of disadvantages. First, the definition of the anaerobic capacity parameter does not account for varying energy depletion or power decay rates of the physiological process that actually occurs as the body progresses through various exercise states, specifically through anaerobic energy producing states. Secondly, the peak power value produced by this test protocol may be inaccurate and, thus, misleading, since considerable undetected changes in power output may occur during a 5-second sampling subinterval.
Comparing an aerobic treadmill test and an anaerobic bicycle test illustrates that the former stems from interest in the work potential of the heart, e.g., cardiac performance, while the latter originates from interest in the work potential of the body, e.g., mechanical performance. It is desirable to provide an accurate measure of anaerobic capacity as an indication of the subject's capacity to produce energy via anaerobic metabolism as well as an indication of the state of the specific muscle types that draw energy from anaerobic metabolism.
The mathematical model for the natural decay of total power is described as follows: EQU P.sub.total =P.sub.1 +P.sub.2 +P.sub.3 +. . . P.sub.n,
where each metabolic component is P.sub.i =e.sup.k i.sup.t. The first approximation that assumes that one metabolic power source is dominant in the contribution of power is expressed as P.sub.total =e.sup.-kt.
By design of the present invention, the anaerobic lactate metabolism is emphasized in the production of power. By imposing a heavy load on the subject that far exceeds the subject's aerobic power capabilities, the aerobic component of the total power is minimized. By extending the length of the test well beyond the expected depletion time of the aerobic creatinine phosphate metabolism, the dominant component of the power decay that is measured represents the power decay of the anaerobic lactate metabolism.
The present invention provides a definition of an anaerobic capacity parameter that is related to the subject's capacity to produce energy via anaerobic metabolism. The invention also provides a method and apparatus that provide a quick and meaningful assessment of anaerobic exercise parameters. These parameters include anaerobic capacity (anaerobic endurance time), will power, total work, peak power, potential power, stamina, average power, and fade. When compared to an isolated aerobic view of human activity, the exercise parameters of the present invention have many practical applications, e.g., monitoring daily activities, special work demands, athletic achievement, and rehabilitation. The present invention provides a simple, brief, noninvasive method and apparatus for determining the anaerobic capacity of an individual.